1. Field of the Invention
The present invention relates to a sprayed coating formed inside a semiconductor processing device and relates to a production method for the same, and in particular, relates to a production technique for producing a sprayed coating in which excellent electrical insulation and corrosion resistance are simultaneously obtained.
2. Description of Related Art
When a deposit is formed on metallic material by ceramic-spray forming, heat resistance, electrical insulation, and corrosion resistance of the material surface can be created or increased. Therefore, a coating formation technique such as a ceramic-spray forming is applied to numerous technical field such as aviation, nuclear energy and semiconductors. In these coating formation techniques, particularly when a material having high melting point is sprayed on a surface of a metallic material, plasma spraying is utilized in which a plasma arc or a plasma jet having high heat energy is a heat reservoir. The plasma spraying is a method in which an arc is generated between an anode and a cathode, and melted material is jetted out to the exterior with carrier gas by a nozzle. As the carrier gas, a gas in which hydrogen or nitrogen is mixed with argon gas is generally utilized in addition to inert gases such as argon gas or helium gas.
As mentioned above, electrical insulation and corrosion resistance in various sprayed coatings formed by the plasma spraying are inferior to those in sintered compacts obtained by sintering the same material. This is because many vacancies are in the sprayed coating and the sprayed coating has oxygen defects.
Therefore, techniques, in which the size and number of vacancies is decreased, whereby the sprayed coating is densified, are variously proposed. In these techniques, for example, a method in which plasma spraying is performed on fine powder under reduced pressure, whereby the sprayed coating is densified is proposed (for example, see Japanese Laid-Open Patent Publication No. HEI 10-226869 (pages 4 and 5, and FIG. 1)).
In the method described in the above patent document, sprayed coating can be densified. However, the condition of the oxygen defects of the sprayed coating cannot be suppressed because plasma spraying is performed under reduced pressure. When the sprayed coating which has oxygen defects is utilized in a sprayed-coating portion formed inside the semiconductor processing device, the sprayed coating is a semiconductor during use of the semiconductor processing device, whereby volume resistivity of the sprayed coating is decreased. Accordingly, in this case, excellent electrical insulation cannot be obtained. Moreover, the condition of the oxygen defects is more unstable thermodynamically than the condition of the stoichiometric composition, whereby the sprayed coating is highly reactive in the utilization of the semiconductor processing device, resulting in being poor in corrosion resistance. Therefore, recently, development of production techniques for sprayed coatings, in which the above-mentioned problem in the oxygen defects is solved, whereby excellent electrical insulation and corrosion resistance can be simultaneously obtained, is desired.